On Mon, Jun 04, 2018 at 10:57:05PM +0200, Eric Botcazou wrote:
> > In the PR we have insns:
> > 
> > Trying 23 -> 24:
> >    23: r123:SI=zero_extend(r122:HI)
> >       REG_DEAD r122:HI
> >    24: [r115:SI]=r123:SI
> >       REG_DEAD r123:SI
> > 
> > which should be combined to
> > 
> > (set (mem:SI (reg/f:SI 115 [ pretmp_19 ]) [1 *pretmp_19+0 S4 A32])
> >     (and:SI (subreg:SI (reg:HI 122) 0)
> >         (const_int 32767 [0x7fff])))
> > 
> > But nonzero_bits of reg:HI 122 is 0x7fff, and nonzero_bits1 thinks it
> > then also has that same nonzero_bits for the subreg.  This is not
> > correct: the bit outside of HImode are undefined.  load_extend_op
> > applies to loads from memory only, not anything else.  Which means the
> > whole AND is optimised away.
> 
> No, this is done on purpose for WORD_REGISTER_OPERATIONS targets and your 
> patch will pessimize them.  I'm going to have a look at the PR then.

Hi Eric,

Do you have any progress with this?


Segher

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